The obesity epidemic is a global phenomenon that does not respect geographic or socio-demographic boundaries. Thus, research on factors related to the obesity epidemic has focused on social and economic characteristics of modern societies. This article discusses obesity in Spain and trends in several associated factors. Together with the increase in the prevalence of obesity, important changes in the population's dietary pattern have been observed, although total energy and fat intake appear to be stable. According to several indirect indicators, sedentary behavior predominates, although the percentage of the population reporting some leisure exercise is increasing. An increase in the amount of leisure time in modern societies is suggested as an explanation for this paradox. Factors related to energy expenditure could be as important as dietary factors in the genesis of the obesity epidemic.